[..] Pact Magic without any rest is awful. It's almost worse than an EB/AT 1/3 caster.
Pact Magic with one rest is almost equal to half caster. Admittedly, it maintains a solid lead through most of the progression (finally falling behind only at 15th level) but the half-caster pulls within a point or so several times.
Pact Magic with two rests keeps pace with a full caster for the first ten levels, but after that falls bending hard. Topping out at the equivalent of a 13th level caster. Again, MA would make up a lot of slack on this (effectively emulating 43 additional points worth of high-level spells right around the same time a full caster gets them) but the limited nature of MA doesn't quite equal the full caster's range of high-level magic.
[..]
I think it also shows why people have such wildly different experiences with the class. If you were in a game with frequent short breaks, the warlock felt on par with the other main casters. If you were in a game with few or no short rests, you were playing with one hand tied behind your back.